I saw the Prophet ﷺ praying voluntary prayers on his mount, facing whichever direction it took, but he would make the prostration lower than the bowing, performing both with gestures.
حدثنا عبد الرزاق أخبرنا ابن جريج أخبرني أبو الزبير أنه سمع
رأيت النبي ﷺ يصلي وهو على راحلته النوافل في كل جهة ولكنه يخفض السجود من الركعة ويومئ إيماء
Its isnad is sahih. It is found in Bukhari 4/436 no. 2257, Fath al-Bari, in the chapter on right of preemption, right of preemption in what has not been divided, Abu Dawud 3/784 no. 3514, in the chapter on sales, right of preemption, Tirmidhi 3/652 no. 1370, in the chapter on rulings, right of preemption, where he said, hasan sahih, and Ibn Majah 2/834 no. 2497.